The purpose of this study is analyzed the impact of oxygen adjusted during exercise in COPD patients without conventional for LTOT but with exercise desaturation.

Oxygen will be administered through nasal cannulae. Patients will be provided with a tank of liquid oxygen and a rechargeable portable device. The 6 minuts walking test will be used to adjusted oxygen flow in the GFA group (to achieve a mean SpO2 ≥ 90%). In the control group (GC), a 3L/min oxygen flow will be administer. Oxygen is used when the patient perform physical activity. The treatment period for each patient is 6 months (3 months in the GC grup, 3 months in the GFA one).

Inclusion Criteria:

• Clinical stable moderate to severe COPD (FEV1 <70%, FEV 1 / FVC <70%) total lung capacity (TLC> 80%) without conventional criteria for LTOT, optimal medical therapy, mean SpO2 ≤ 88% during the 6 minuts walking test and active life outside the home, other than active smoking or are in program respiratory rehabilitation.

Exclusion Criteria:

• Current smokers - Presence of respiratory failure and criteria for LTOT (PO2 <55 mmHg or 55-60 mmHg associated with pulmonary arterial hypertension, chronic cor pulmonale, congestive heart failure, arrhythmias or polycythemia). - Presence of impaired mobility - Cognitive impairment or intellectual disability to fill in questionnaires - No acceptance of liquid oxygen - Presence of active comorbidities (cardiovascular disease, rheumatologic, renal, hepatic) - Participation in pulmonary rehabilitation programs